1. Field of the Invention
The present invention relates to apparatus for driving a display panel to display an image based on an input image signal.
2. Description of the Related Art
A common type of display panel is an active matrix liquid crystal display panel having m scanning lines extending horizontally and n source lines extending vertically across a two-dimensional liquid crystal display screen, where m and n are integers greater than one. Pixel electrodes are located at the intersections of the source and scanning lines. Also located at each such intersection is a transistor through which the voltage on the source line is applied to the pixel electrode. Each scanning line is connected to the gates of n of these transistors.
This type of liquid crystal display panel has a source driver that generates n voltages corresponding to the brightness levels to be displayed by the n pixels on one scanning line and applies these voltages to the source lines, as described, for example, by Date et al. in Japanese Patent Application Publication No. 2001-034233. To prevent degradation of the liquid crystal material, the source driver periodically switches the polarity of the voltages applied to the liquid crystal. The switching is carried out so that of each two adjacent source lines, one receives a voltage with positive polarity, the other receives a voltage with negative polarity, and these polarities are reversed at regular intervals.
If the polarity reversals are effected with switching elements located between the selectors that select the output potentials and the amplifiers that amplify the selected output potentials and drive the source lines, as taught by Date et al., then each amplifier must be designed for output of potentials of both positive and negative polarity. In addition, immediately following a polarity switchover, there is a momentary large flow of current through the amplifiers to charge or discharge the capacitance of the liquid crystal panel. This unwanted current flow distorts the voltage waveforms applied to the source lines and impairs the quality of the displayed image.
This problem could be addressed by supplying switches between the amplifiers and the source lines to disconnect the amplifiers from the source lines, and further switches to restore the source lines to a common potential, as taught by Kodama et al. in U.S. Pat. No. 7,304,632, but it would then be necessary to provide and control a large number of additional switching elements.